The present invention relates to a phono pickup cartridge having an interchangeable stylus unit and a cartridge body. The invention relates more particularly to positioning device which is mounted between the interchangeable stylus unit and the cartridge body for phono pickup cartridges.
In phono pickup cartridges, it is highly desired that a movable induction generating member thereof be disposed accurately at a predetermined position in narrow magnetic gaps formed in a cartridge body. Therefore, a strong and accurate positioning device is required in order to prevent generation of undesired vibration due to resonance or the like.
In order to satisfy the above-described requirement, there has been proposed, for example, a positioning device as described in U.S. Pat. No. 3,761,647. As disclosed in that patent, a stereophonic pickup cartridge is provided with a positioning device between a stylus unit and a pickup cartridge body. The stylus unit has a post-shaped plug having therein a groove while the cartridge body has therein an aperture adapted to receive the post-shaped plug. When the stylus unit is mounted on the cartridge body, the post-shaped plug is inserted into the aperture with the groove of the post-shaped plug engaged with an annular lock ring in the aperture made of elastomeric material to thereby ensure alignment.
However, with such a construction, since the stylus unit is simply engaged with the cartridge body, the post-shaped plug can rotate around its center axis and the stylus unit can be displaced in the axial direction of the cantilever. As a result, the stylus unit must be secured to the cartridge body to prevent deviation from the correct position. This leads to a difficulty in reproducing stereophonic sound, and distortion and resonance problems are present.